Assuming you drive 500 miles per day and you drove everyday then you would drive around 15,000 miles in one month.
So then at 15,000 miles per month it would take you around 6 or 7 months to drive 100,000 miles.
Of course you would probably take a break and not want to drive on some days if you drove on a 100,000 mile road trip.
But expect it to take between 7 to 10 months to drive 100,000 miles and maybe as long as 1 year.
However if you just drove your vehicle 1,000 miles each month then it would mean you would drive 12,000 miles in a year.
So for that driving you would drive the 100,000 miles in around 8 years of driving.
I average around 1,000 miles per month driving so that's 12,000 miles in a year so it would take me 8 years roughly to rack up 100,00 miles.